The present invention relates generally to the field of filters and, in particular, to a tunable resonator for a filter.
Wireless telecommunications systems transmit signals to and from wireless terminals using radio frequency (RF) signals. A typical wireless system includes a plurality of base stations that are connected to the public switched telephone network (PSTN) via a mobile switching center (MSC). Each base station includes a number of radio transceivers that are typically associated with a transmission tower. Each base station is located so as to cover a geographic region known colloquially as a xe2x80x9ccell.xe2x80x9d Each base station communicates with wireless terminals, e.g. cellular telephones, pagers, and other wireless units, located in its geographic region or cell.
A wireless base station includes a number of modules that work together to process RF signals. These modules typically include, by way of example, mixers, amplifiers, filters, transmission lines, antennas and other appropriate circuits. One type of filter that finds increased use in wireless base stations is known as a microwave cavity filter. These cavity filters include a number of resonators formed in a plurality of cavities so as to provide a selected frequency response when signals are applied to an input of the filter.
Each resonator in a filter is tuned to have a selected resonant frequency. Many techniques are conventionally available for remotely tuning the resonant frequency of these filters. These techniques include electromagnetic actuators and stepper motors. Unfortunately, these techniques each have limitations and drawbacks. For example, many of the remote tuning techniques have a limited tuning range or require large movement amplitudes to gain the required tuning range. Further, many of the remote tuning techniques are not reliable.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an improved tunable resonator.
The above-mentioned problems with tunable resonators and other problems are addressed by embodiments of the present invention and will be understood by reading and studying the following specification. Embodiments of the present invention provide a tunable resonator that is tuned by varying the size of a gap between a resonator body and a ground plane, or a portion of a ground plane, of the resonator.
More particularly, in one embodiment a tunable resonator is provided. The resonator includes a housing having a cavity. A resonator body is disposed adjacent to a first surface within the cavity. A gap is formed between the resonator body and the first surface. The resonator is tuned by controlling the size of the gap.